The present invention relates to a feed roll assembly adapted for use in a fax machine or the like and controlled to feed sheet of paper.
A variety of fax machines have been disclosed, and have appeared on the market. Regular fax machines commonly have a feed roll assembly driven to feed paper into the machine. FIG. 1 shows the feed roll assembly of a regular fax machine. As indicated, the feed roll assembly comprises an axle, a roll fixedly mounted around the axle in the middle, a transmission gear revolvably mounted around one end of the axle and coupled to a motor drive, a coupling wheel mounted around the axle adjacent to the transmission gear and turned with the axle, and a spring mounted around the coupling wheel and connected to the transmission gear. When the transmission gear is rotated forwards, the spring is compressed, causing the coupling wheel and the spring to be coupled together by means of a friction force, and therefore the coupling wheel is driven by the transmission gear to turn the axle. When the axle is rotated, the inserted sheet of paper is fed by the roll to the transmission roll inside the fax machine. The transmission roll is turned at a higher speed. When the sheet of paper is delivered forwards by the transmission roll, the spring is released from the coupling wheel to cut off power transmission between the transmission gear and the coupling wheel. Because the coupling between the spring and the coupling wheel is achieved by means of a friction force, the precision of the spring and the coupling wheel is critical. Therefore, the manufacturing cost of the feed roll assembly is expensive. Furthermore, in order to let inserted sheets of paper to be separately delivered one after another, the speed ratio between the roll of the axle and the transmission roll must be big enough. However, increasing the speed ratio between the roll of the axle and the transmission roll tends to cause the fed sheet of paper to be deviated from the course.